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Many studies have shown that starting young mice on a restricted-calorie diet helps them live for months longer than lab animals fed a standard diet. But the new research shows that even 19-month-old mice, about the human equivalent of 60 to 65 years, can have a longer life when eating fewer calories. The study appears this week in the Proceedings of the National Academy of Sciences.

Researchers led by Stephen R. Spindler of the University of California, Riverside, found that restricting calories for old mice had an immediate benefit in slowing the aging process and that eventually the animals lived up to six months longer than their litter mates who were fed the standard diet.

The diet change added about 42 percent to the remaining life span of the calorie-restricted mice when compared with the others, said Spindler.

It’s still unproven that calorie restriction would extend life in humans as it does in mice, said Spindler, but if the findings do translate to people “this could mean a lot more years and a lot of good years. The mice on caloric restriction live longer and they are healthier.”

Spindler said that while older mice who go on a diet do live longer than those who don’t, they still don’t live as long as mice that have been on restricted diets for a lifetime. He said mice put on low-calorie diets just after birth have been known to live up to four years, almost twice as long as normal mice and months longer than the aged mice in the new study.

The message, he said, is that sensible eating for a lifetime is best, but there are life span benefits even if the diet is not started until old age.

“This is a very important finding,” said Dr. George S. Roth of the National Institute on Aging, one of the National Institutes of Health.

Better late than never
“The dogma has always been that the earlier in life you start a restricted diet, the better it works for extending life,” said Roth, a researcher studying the aging process who was not involved in Spindler’s research. “This finding suggests that you may get some of the same benefits starting late in life.”

Spindler said the study also found that the restricted-calorie diets also slowed the development and advancement of cancer. Death from tumors is very common among aged mice, he said, but the researchers found that tumor growth either started later or was slowed among mice fed limited calories.

The researchers also analyzed how the action of genes changed in mice placed on restricted calorie diets. Spindler said there were changes and that these might be biomarkers of how the restricted diet works to extend life.

“People have been searching for 30 years for biomarkers of the changes that take place during the aging process,” said Spindler. He said the new study in mice suggests that by measuring gene expression — the amount and type of proteins made by the genes — scientists could pinpoint the biomarkers of aging.

Once those are known, he said, it would be possible to find drugs that have the same effect on life extension as calorie-restricted diets.

Does this mean that eventually aging could be slowed by taking a pill?